Private:video broadcasting ideas
From NMSL
Research problems related to video streaming and broadcasting in WiMAX networks.
Statistical Multiplexing
Statistical Multiplexing aims to better utilize the link bandwidth by multiplexing the data rate variabilities of multiple streams in time domain. When bandwidth is less than the aggregated data rate of the multiplexed streams the individual streams need to be adapted/rate shaped/bit extracted. Some of the related challenges are noted below.
- The first challenge is to estimate the importance of each stream in the congestion window and allocate a proportionate target bit rate for adaptation. The challenge is harder if the original video sequence is not available as a reference for quality or complexity calculations. In this scenario we have to resort to methods of no-reference quality/complexity estimation.
- No-reference quality estimation itself is a challenging task. Two main approaches in practice are (1) Sending a metadata stream out of band which contains the necessary information generated by the encoder and (2) The encoder embeds some supplementary information in the compressed bit stream itself( SEI units in H.264). Both have their pros and cons. For a comparative analysis see [1]. One thing common between both the schemes is that the encoder supplies the hints or metadata. The problem of estimation solely on the basis of the compressed stream (i.e. without using even the SEI information, only using the mandatory parts) is not explored.
- A third challenge is to find a model of estimation window. Since in modern encoding standards the frames or access units have complex relationships with many frames in past and future it is not possible to estimate each frames importance independently. Look-ahead and feed-back are two common approaches used my majority of work so far. Are the two approaches sufficient individually? If not what mix should we use in a hybrid approach.
- Finally, for slot based networks(e.g. OFDMA) the rate adapted streams cannot be transmitted as is, they need to be converted into bursts in order to be allocated in the slots. What burst creation allocation policy should we take here. We note that at this point we are not considering energy efficiency of the allocation. We are considering the challenge of packet fragmentation under deadline constraints. Can this consideration be incorporated into the target rate decision process so that after adaptation again data is not lost due to infeasible scheduling instances.
Energy Efficient MBS Allocation
Other Ideas
- Energy and video quality optimization for receivers. Note that not all receivers will be handheld mobile devices. Some WiMAX receivers could be static desktops, which do not have energy problem. Do we have separate streams for different types of receivers? Or should we look for a tradeoff between energy optimization (for mobile devices) and channel switching delay (for all receivers)?
- How do we allocate the wireless medium (downlink and uplink)? Keep in mind that other services from WiMAX subscribers can also be running. Can we design an efficient scheduler at the base station to provide QoS for video broadcasting as well as other services?
- How we can exploit/optimize WiMAX's mobile handoffs in a mobile environment for video broadcasting and other services.
- Performance Evaluation of Multicast/Broadcast Single Frequency Network Operation for WiMAX. Using resource efficient transport formats and assuming perfect synchronization among the BS can achieve almost twice the spectral efficiency of conventional cellular network. There is a similar evaluation for WCDMA networks but not much work has been done for WiMAX.
- Minimize energy consumption by reducing number of sleep-wakeup transitions.
- Video in WiMAX can be delivered over unicast, multicast or broadcast channels. While broadcast is more resource efficient, unicast offers more flexibility in terms of user specific content. According to the users video request the BSS can decide to add the user to a unicast, multicast or broadcast group. How does this decision making improve the quality of video transmission? Does this help in increasing the network capacity? Since different mode of transmission require different amount of power, are there any implications in terms of Base Station power efficiency?
Challenge1: Finding typical video viewing pattern statistics as test data.
- Multimedia Overlay Construction over WiMAX:
